This invention generally relates to the fabrication of electrical interconnectors used to electrically connect printed circuit boards and other electrical components in a vertical or z-axis direction to form three-dimensional electronic modules. More particularly, the present invention relates to a new and improved machine and method for fabricating z-axis interconnectors of the type formed from helically coiled strands of wire, in which at least one longitudinal segment of the coiled strands is untwisted in an anti-helical direction to expand the strands of wire into a resilient bulge. Bulges of the interconnector are then inserted into vias of vertically stacked printed circuit boards to establish an electrical connection through the z-axis interconnector between the printed circuit boards of the three dimensional module.
The evolution of computer and electronic systems has demanded ever-increasing levels of performance. In most regards, the increased performance has been achieved by electronic components of ever-decreasing physical size. The diminished size itself has been responsible for some level of increased performance because of the reduced lengths of the paths through which the signals must travel between separate components of the systems. Reduced length signal paths allow the electronic components to switch at higher frequencies and reduce the latency of the signal conduction through relatively longer paths. One technique of reducing the size of the electronic components is to condense or diminish the space between the electronic components. Diminished size also allows more components to be included in a system, which is another technique of achieving increased performance because of the increased number of components.
One particularly effective approach to condensing the size between electronic components is to attach multiple semiconductor integrated circuits or xe2x80x9cchipsxe2x80x9d on printed circuit boards, and then stack multiple printed circuit boards to form a three-dimensional configuration or module. Electrical interconnectors are then extended vertically, in the z-axis dimension, between the printed circuit boards which are oriented in the horizontal x-axis and y-axis dimensions. The z-axis interconnectors, in conjunction with conductor traces of each printed circuit board, connect the chips of the module with short signal paths for efficient functionality. The relatively high concentration of chips, which are connected by the three-dimensional, relatively short length signal paths, are capable of achieving very high levels of functionality.
The vertical electrical connections between the stacked printed circuit boards are established by using z-axis interconnectors. Z-axis interconnectors contact and extend through plated through holes or xe2x80x9cviasxe2x80x9d formed in each of the printed circuit boards. The chips of each printed circuit board are connected to the vias by conductor traces formed on or within each printed circuit board. The vias are formed in each individual printed circuit board of the three-dimensional modules at the same locations, so that when the printed circuit boards are stacked in the three-dimensional module, the vias of all of the printed circuit boards are aligned vertically in the z-axis. The z-axis interconnectors are then inserted vertically through the aligned vias to establish an electrical contact and connection between the vertically oriented vias of each module.
Because of differences between the individual chips on each printed circuit board and the necessity to electrically interconnect to the chips of each module in a three-dimensional sense, it is not always required that the z-axis interconnectors electrically connect to the vias of each printed circuit board. Instead, those vias on those circuit boards for which no electrical connection is desired are not connected to the traces of that printed circuit board. In other words, the via is formed but not connected to any of the components on that printed circuit board. When the z-axis interconnector is inserted through such a via, a mechanical connection is established, but no electrical connection to the other components of the printed circuit board is made. Alternatively, each of the z-axis interconnectors may have the capability of selectively contacting or not contacting each via through which the interconnector extends. Not contacting a via results in no electrical connection at that via. Of course, no mechanical connection exists at that via either, in this example.
A number of different types of z-axis interconnectors have been proposed. One particularly advantageous type of z-axis interconnector is known as a xe2x80x9ctwist pin.xe2x80x9d Twist pin z-axis interconnectors are described in U.S. Pat. Nos. 5,014,419, 5,064,192, and 5,112,232, all of which are assigned to the assignee hereof.
An example of a prior art twist pin 50 is shown in FIG. 1. The twist pin 50 is formed from a length of wire 52 which has been formed conventionally by helically coiling a number of outer strands 54 around a center core strand 56 in a planetary manner, as shown in FIG. 2. At selected positions along the length of the wire 52, a bulge 58 is formed by untwisting the outer strands 54 in a reverse or anti-helical direction. As a result of untwisting the strands 54 in the anti-helical direction, the space consumed by the outer strands 54 increases, causing the outer strands 54 to bend or expand outward from the center strand 56 and create a larger diameter for the bulge 58 than the diameter of the regular stranded wire 52. The laterally outward extent of the bulge 58 is illustrated in FIG. 3, compared to FIG. 2.
The strands 54 and 56 of the wire 52 are preferably formed from beryllium copper. The beryllium copper provides necessary mechanical characteristics to maintain the shape of the wire in the stranded configuration, to allow the outer strands 54 to bend outward at each bulge 58 when untwisted, and to cause the bulges 58 to apply resilient radial contact force on the vias of the printed circuit boards. To facilitate and enhance these mechanical properties, the twist pin will typically be heat treated after it has been fabricated. Heat treating anneals or hardens the beryllium copper slightly and tempers the strands 54 at the bulges 58, causing enhanced resiliency or spring-like characteristics. It is also typical to plate the fabricated twist pin with an outer coating of gold. The gold plating establishes a good electrical connection with the vias. To cause the gold-plated exterior coating to adhere to the twist pin 50, usually the beryllium copper is first plated with a layer of nickel, and the gold is plated on top of the nickel layer. The nickel layer adheres very well to the beryllium copper, and the gold adheres very well to the nickel.
The bulges 58 are positioned at selected predetermined distances along the length of the wire 52 to contact the vias 60 in printed circuit boards 62 of a three-dimensional module 64, as shown in FIG. 4. Contact of the bulge 58 with the vias 60 is established by pulling the twist pin 50 through an aligned vertical column of vias 60 in the module 64. The outer strands 54 of the wire 52 have sufficient resiliency when deflected into the outward protruding bulge 58, to resiliently press against an inner surface of a sidewall 66 of each via 60, and thereby establish the electrical connection between the twist pin 50 and the via 60, as shown in FIG. 5. In those circumstances where an electrical connection is not desired between the twist pin 50 and the components of a printed circuit board, the via 60 is formed but no conductive traces connect the via to the other components of the printed circuit board. One such via 60xe2x80x2 is shown in FIG. 4. The sidewall 66 of the via 60xe2x80x2 extends through the printed circuit board, but the via 60xe2x80x2 is electrically isolated from the other components on that printed circuit board because no traces extend beyond the sidewall 66. Inserting a bulge 58 of the twist pin 50 into a via 60xe2x80x2 that is not connected to the other components of a printed circuit board eliminates an electrical connection from that twist pin to that printed circuit board, but establishes a mechanical connection between the twist pin and the printed circuit board which helps support and hold the printed circuit board in the three-dimensional module.
To insert the twist pins 50 into the vertically aligned vias 60 of the module 64 with the bulges 58 contacting the inner surfaces 66 of the vias 60, a leader 68 of the regularly-coiled strands 54 and 56 extends at one end of the twist pin 50. The strands 54 and 56 at a terminal end 70 of the leader 68 have been welded or fused together to form a rounded end configuration 70 to facilitate insertion of the twist pin 50 through the column of vertically aligned vias. The leader 68 is of sufficient length to extend through all of the vertically aligned vias 60 of the assembled stacked printed circuit boards 62, before the first bulge 58 makes contact with the outermost via 60 of the outermost printed circuit board 62. The leader 68 is gripped and the twist pin 50 is pulled through the vertically aligned vias 60 until the bulges 58 are aligned and in contact with the vias 60 of the stacked printed circuit boards. To position the bulges in contact with the vertically aligned vias, the leading bulges 58 will be pulled into and out of some of the vertically aligned vias until the twist pin 50 arrives at its final desired location. The resiliency of the strands 54 allow the bulges 58 to move in and out of the vias without losing their ability to make sound electrical contact with the sidewall of the final desired via into which the bulges 58 are positioned. Once appropriately positioned, the leader 68 is cut off so that the finished length of the twist pin 50 is approximately at the same level or slightly beyond the outer surface of the outer printed circuit board of the module 64. A tail 72 at the other end of the twist pin 50 extends a shorter distance beyond the last bulge 58. The strands 54 and 56 at an end 74 of the tail 72 are also fused together. The length of the tail 72 positions the end 74 at a similar position to the location where the leader 68 was cut on the opposite side of the module. However, if desired, the length of the tail 72 or the remaining length of the leader 68 after it was cut may be made longer or shorter. Allowing the tail 72 and the remaining portion of the leader 68 to extend slightly beyond the outer printed circuit boards 62 of the module 64 facilitates gripping the twist pin 50 when removing it from the module 64 to repair or replace any defective components. In those circumstances where it is preferred that the ends of the twist pin do not extend beyond the outside edges of the three-dimensional module, an overlay may be attached to the outermost printed circuit boards to make the ends of the twist pin flush with the overlay.
The ability to achieve good electrical connections between the vias 60 of the printed circuit boards depends on the ability to precisely position the location of the bulges 58 along the length of wire 52. Otherwise, the bulges 58 would be misaligned relative to the position of the vias, and possibly not create an adequate electrical connection. Therefore, it is important in the formation of the twist pins 50 that the bulges 58 be separated by predetermined intervals 76 (FIG. 1) along the length of the wire 52. The position of the bulges 58 and the length of the intervals 76 depend on the desired spacing between the printed circuit boards 62 of the module 64. The amount of bending of each of the outer conductors 54 at each bulge 58 must also be controlled so that each of the bulges 58 exercises enough force to make good electrical contact with the vias. Moreover, the amount of outward deflection or bulging of each of the bulges 58 must be approximately uniform so that none of the bulges 58 experiences permanent deformation when the bulge is pulled through the vias. Distortion-induced disparities in the dimensions of the bulges adversely affect their ability to make sound electrical connections with the vias 60. Further still, each twist pin 50 should retain a coaxial configuration along its length without slight angular bends at each bulge and without any bulge having asymmetrical characteristics. The coaxial configuration facilitates inserting the twist pin through the vertically aligned vias, maintaining the resiliency of the bulges, and establishing good electrical contact with the vias.
The requirements for close tolerances and precision in the twist pins are made more significant upon recognizing the very small size of the twist pins. The typical sizes of the most common sizes of helically-coiled wire are about 0.0016, 0.0033 and 0.0050 in. in diameter. The diameters of the strands 54 and 56 used in forming these three sizes of wires are 0.005, 0.0010, and 0.0015 in., respectively. The typical length of a twist pin having four to six bulges which extends through four to six printed circuit boards will be about 1 to 1.5 inches. The outer diameter of each bulge 58 will be approximately two to three times the diameter of the regularly stranded wire in the intervals 76. The tolerance for locating the bulges 58 between intervals 76 is in the neighborhood of 0.002 in. The weight of a typical four-bulge twist pin is about 0.0077 grams, making it so light that handling the twist pin is very difficult. Handling each twist pin is also complicated because its small dimensions do not easily resist the forces that are necessary to manually manipulate the twist pin without bending or deforming it. It is not unusual that a complex 4 in.xc3x974 in. module 64 may require the use of as many as 22,000 twist pins. Thus, the relatively large number of twist pins necessary to assemble each three-dimensional module require an ability to fabricate a relatively large number of the twist pins in an efficient and rapid manner.
A general technique for fabricating twist pins is described in the three previously-identified U.S. patents. That described technique involves advancing the length of the stranded wire, clamping the stranded wire above and below the location where the bulge is to be formed, fusing the outer strands of the wire to the core strand of the wire preferably by laser welding at the locations above and below the bulge, and rotating the wire between the two clamps in an anti-helical direction to form the bulge.
In a prior art implementation of this twist pin fabrication technique, a wire feeder advanced an end of the helically stranded wire which was wound on a spool. The wire feeder employed a lead screw mechanism driven by an electric motor to advance the wire and unwind it from the spool. A solenoid-controlled clamp was connected to the lead screw mechanism to grip the wire as the lead screw mechanism advanced as much of the stranded wire from the spool as was necessary for use at each stage of fabrication of the twist pin. To advance more wire, the clamp opened and the lead screw mechanism retracted in a reverse movement. The clamp then closed again on the wire and the electric motor again advanced the lead screw mechanism.
While this prior art wire feeder mechanism was functional, the reciprocating movement of the feeder mechanism reduced efficiency and slowed the speed of operation. Half of the reciprocating movement, the return movement to the beginning position, was wasted motion. Moreover, the relatively high inertia and mass of the lead screw, clamp and motor armature required extra force and hence time to execute the reversing movements necessary for reciprocation. Furthermore, the rotational mass of the wire wound on the spool limited the acceleration rate at which the lead screw could unwind the wire off of the spool. The rotational mass was frequently sufficient enough to cause the wire to slip in the clamp carried by the lead screw. Slippage at this location resulted in the formation of the bulges at incorrect positions and incorrect lengths of the leader 68 and the internal lengths 76. The desire to avoid slippage also limited the operating speed of the fabricating equipment.
The prior art bulge forming mechanism included two clamping devices which closed on the wire above and below at the location where each bulge was to be formed. The clamping devices held a wire while a laser beam fused the outer strands 54 to the center core strand 56 at those locations. Thereafter, the lower clamping device was rotated in an anti-helical direction while the upper clamping device held the wire stationary, thereby forming the bulge 58.
The lower clamping device was carried by a sprocket, and the wire extended through a hole in the center of the sprocket. A first pneumatic cylinder was connected to the clamping device to cause the clamping device to grip the wire. A chain extended around the sprocket and meshed with the teeth of the sprocket. One end of the chain was connected to a spring, and the other end of the chain was connected to a second pneumatic cylinder. When the second pneumatic cylinder was actuated, its rod and piston pulled the chain to rotate the sprocket by the amount of the piston throw. Upon reaching the end of its throw, the rod and cylinder of the second pneumatic cylinder was returned in the opposite direction to its original position by the force of the spring which pulled the chain in the opposite direction. Of course, moving the chain to its original position also rotated the sprocket in the opposite direction to its original position.
After gripping the wire by activating the first pneumatic cylinder, the second pneumatic cylinder was activated to rotate the sprocket in the anti-helical direction. However, the throw of the second pneumatic cylinder, and the amount of rotation of the sprocket, was insufficient to completely form a bulge with a single rotational movement. Instead, two separate rotational movements were required to completely form the bulge. After the rotation, the lower clamping device released its grip on the wire while the sprocket rotated in the reverse direction. Upon rotating back to the initial position again, the lower clamping device again gripped the wire and another rotational movement of the sprocket and gripping device was executed to finish forming the bulge.
By providing only a limited amount of rotational movement so as to require two rotations to form the bulge, a significant amount of time was consumed in forming each bulge. The latency of reversing the movement of the components and executing multiple bulge forming movements slowed the fabrication rate of the twist pins. The rotational mass of the sprocket and the clamping mechanism with its attached solenoid activation clamping device reduced the rate at which these elements could be accelerated, and also constituted a limitation on the speed at which twist pins could be fabricated. Apart from the rotational mass issues, acceleration had to be limited to avoid inducing wire slippage. The need to reverse the direction of movement of numerous reciprocating components limited the rate at which the twist pins bulges could be fabricated.
After formation of the bulges in the prior art twist pin fabricating machine, the wire with the formed bulges was cut to length to form the twist pin. The leader of the twist pin extended into a venturi through which gas flowed. The effect of the gas flowing through the venturi was to induce a slight tension force on the wire, and hold it while a laser beam severed the wire at the desired length. The laser beam fused the ends 70 and 74 of the strands 54 and 56 as it severed the fabricated twist pin from the length of wire. The tension force induced on the wire by the gas flowing through the venturi propelled the twist pins into a random pile called a xe2x80x9chaystack.xe2x80x9d After a sufficient number of twist pins had accumulated, they were placed into a separate sorting and singulating machine which ultimately delivered the twist pins one at a time in a specific orientation into a carrier. The pins were later heat treated and transferred from the carrier and inserted into the three-dimensional modules.
The process of sorting the twist pins, orienting them, delivering them into the carrier, and making sure that the twist pins were received properly within the carrier required considerable human intervention and machine handling after the twist pins were fabricated. Occasionally the twist pins would be lodged in tubes which guided the twist pins into the carrier by an air flow. Delivering the twist pins into the receptacles in the carrier was also difficult, and human intervention was required to assure that the twist pins were properly received in the receptacles. Twist pin sorting also occasionally resulted in jamming and bending the twist pins. In general, the post-fabrication processing steps required to organize the twist pins for their subsequent use contributed to overall inefficiency.
These and other considerations pertinent to the fabrication of twist pins have given rise to the new and improved aspects of the present invention.
One improved aspect of the present invention involves a twist pin fabricating machine and a method of fabricating twist pins which produces twist pins more rapidly and more efficiently than previous techniques. Another improved aspect of the present invention involves fabricating twist pins having more uniform and precisely controlled characteristics, such as more precisely positioned bulges, more uniformly and symmetrically shaped bulges, and bulges, leaders, tails and intervals of more precisely controlled dimensions. Another improved aspect of the present invention involves fabricating twist pins without using reciprocal motions. The lost motion of return strokes and the latency associated with reciprocation decreases the speed of fabricating the twist pins. The necessity to accelerate relatively massive components is avoided by using continuous movements or intermittent movements which do not involve changes of direction and which tend to conserve energy and momentum without requiring acceleration of massive components. Another improved aspect is that the nature of the movements involved does not tend to induce slippage of the wire during the fabrication of the twist pin. Other improved aspects of the invention involve efficiently conveying the fabricated twist pins and thereafter storing the twist pins in a manner which allow them to be used, without requiring manual or mechanical sorting and without requiring mechanical contact and possible damage to the fabricated twist pins. Other aspects of the present invention allow the constituent components of the twist pin to be more precisely fabricated into the desired shapes, dimensions and tolerances, while still allowing twist pins of different sizes to be fabricated.
In one principal regard, the present invention relates to a machine for fabricating twist pins from helically coiled to stranded wire. Each twist pin has a plurality of bulges formed at predetermined positions along a segment of wire from which twist pin is fabricated. The machine comprises a wire feed mechanism which receives the stranded wire from a source and includes a roller which frictionally contacts the wire, and a feed motor which rotates the roller while in frictional contact with the wire to advance the wire. The wire feed mechanism advances the wire into a bulge forming mechanism. The wire feed mechanism advances the wire to the predetermined position where the bulge forming mechanism forms a bulge in the wire. The bulge forming mechanism includes first and second controllable clamp members located at spaced apart locations to contact the wire above and below the predetermined position where the bulge is to be formed. The first and second clamp members grip the wire and rotate relative to one another in a anti-helical direction to untwist the wire and form the bulge.
A drive motor rotates the first and second clamp members in complete revolutions relative to one another. At the beginning of a bulge-forming rotational interval, a first and second actuators control the first and second clamp members to grip the wire. During the bulge-forming relative rotational interval the clamp members rotate the wire anti-helically to untwist the helically coiled strands until the strands deflect radially outward to form the bulge. Thereafter at the end of the bulge-forming interval, the first and second actuators control the first and second clamp members to release the grip on the wire. Preferably one of the clamp members is position stationarily and the other clamp member is driven by the motor to rotate relative to it.
In another principal regard, the present invention relates to a method of fabricating twist pins from helically coiled stranded wire. This method comprises the steps of advancing the wire to a predetermined position at which a bulge is to be formed, rotating the wire anti-helically through a continuous rotational interval relative to positions above and below the predetermined position to untwist the helically coiled strands until the strands deflect radially outward to form the bulge, severing a segment of the wire which contains the bulge from a remaining length of the wire to form the twist pin, and conveying the severed twist pin within a flow of gas into a receptacle immediately after severing segment containing the twist pin.
In yet another principal regard, the present invention relates to a method of fabricating twist pins from helically coiled stranded wire. The steps of this method involve comprise gripping the wire at one position with a first controllable clamp member above the location where a bulge is to be formed, gripping the wire at another position with a second controllable clamp member below the location where the bulge is to be formed, rotating the first and second clamp members anti-helically with respect to one another through a continuous bulge-forming rotational interval to untwist the helically coiled strands between the positions into the bulge, controlling the first and second controllable clamp members to release the wire after the relative rotation through the bulge-forming rotational interval, continuing the relative rotation of the first and second clamp members through a wire-advancement rotational interval following the bulge-forming rotational interval, and advancing the wire during the wire-advancement rotational interval.
Preferably, the first and second clamp members are rotated continuously relative to one another during the bulge-forming rotational interval without interruption. The bulge-forming rotational interval is greater than half of a single relative revolution, and is preferably three-fourths of a complete relative revolution. The wire-advancing rotational interval consumes the remaining portion of the relative revolution. A predetermined amount of the wire is advanced during the wire-advancement rotational interval to establish the predetermined position where the next bulge is to be formed. The relative rotation may be slowed or ceased during the wire-advancement interval to accommodate the advancement of precise intervals of wire between bulges and to establish the end of the severed wire segment containing the twist pin.
Another preferable aspect of the present invention involves delivering an amount of slack wire from a source of the wire. The wire is preferably supplied from the source by rotating the roller in frictional contact with the wire. The slack wire forms a predetermined configuration and the wire is advanced from the slack wire configuration when forming the bulges. Establishing the slack wire configuration between the source of the wire, such as a school upon which the stranded wire is wound, isolates the wire advanced to form the bulges from the mass and rotational inertia effects of unwinding the wire from the spool, thereby achieving greater precision without wire slippage in positioning the wire during the formation of the twist pin, as well as achieving greater speed in advancing the wire and consuming less time to advance the wire.
Other preferable features of the invention involve conveying each of a plurality of fabricated twist pins into a separate receptacle of a cassette. The cassette is moved relative to a delivery nozzle through which the fabricated twist pins pass to position an unoccupied receptacle below the delivery nozzle. Preferably, the twist pin is confined in the receptacle of the cassette until it is withdrawn for use. Still other preferable features of the invention involve severing the wire segment and releasing the fabricated twist pin downstream of the location where the bulge is formed, creating a flow of gas sufficient to convey the twist pin after the wire segment is severed and released, conveying the twist pin by the flow of gas into the receptacle of the cassette, and moving the cassette to position an unoccupied receptacle to receive the next fabricated twist pin.
Removing the wire from the source by unwinding the spool independently of advancing the wire, and forming the bulges in a single action in a single rotational interval of a complete relative revolution, and conveying the fabricated twist pins directly into receptacles of a cassette which is moved to position another receptacle to receive each twist pin as it is fabricated, permits twist pins to be fabricated rapidly and efficiently. Moreover the fabricated twist pins have more uniform and precisely positioned and symmetrically shaped bulges. The inefficiency, lost motion and latency associated with reciprocating actions are avoided. The preferred components used to fabricate the twist pins need not be massive and do not require added time and force to accelerate and decelerate. Instead, the preferred components conserve energy and momentum. The risks of wire slippage during advancement and relative rotation are minimized. The fabricated twist pins are efficiently conveyed into the receptacles without requiring mechanical contact or human intervention. The twist pins are stored in receptacles until use, which also eliminates or avoids the risk of damage from manual or mechanical sorting and contact. The machine and the fabrication method are readily adaptable to fabricate twist pins of different sizes.
A more complete appreciation of the present invention and its scope may be obtained from the accompanying drawings, which are briefly summarized below, from the following detailed descriptions of presently preferred embodiments of the invention, and from the appended claims.